The why of yeast's buzz-giving ways

The alcohol in wine, seen here being poured in a file photo for a tasting in Tel Aviv, Israel, is produced by yeast. Scientists are piecing together the evolutionary history of how and why yeast do this, which in turn could lead to new yeast strains for wine and beer fermentation as well as biofuel production.

Wine and beer drinkers of the world owe a lot of gratitude to yeast, the unicellular fungi that ferment sugars to ethanol, giving the fruit- and grain-based drinks their sought-after alcoholic kick. Now, scientists are closing in on just how and why yeast evolved to do this.

No, it wasn't to get humans drunk.

The special trick of yeast is the ability to ferment sugar to 2-carbon components, in particular ethanol, without completely oxidizing it to carbon dioxide, even in the presence of excess oxygen. This allows yeasts to out-compete other microorganisms.

A team of European researchers led by the yeast molecular genetics group at Lund University in Sweden has been trying to reconstruct the evolutionary history of ethanol production. In their latest effort, the team compared the genetic makeup of two wine yeasts: Saccharomyces cerevisiae and Dekkera bruxellensis.

The yeasts separated more than 200 million years ago and are not closely rated. However, the research shows that approximately 100 to 150 million years ago, both yeasts experienced similar environmental conditions and pressure: the appearance of sugar-laden fruits and competition from other microbes.

The pressure, the researchers found, spurred both lineages, independently and in parallel, to develop the ability to make and accumulate ethanol in the presence of oxygen, and developed resistance to high ethanol concentration, and have been using this ability as a weapon to out-compete other microbes which are sensitive to ethanol.

Surprisingly, the team notes, both yeasts used the same molecular tool, global promoter rewiring, to change the regulation pattern of the expression of respiration-associated genes involved in sugar degradation, which allows ethanol to accumulate. The excess ethanol is toxic to other microbes.

"Our results now help to reconstruct the original environment and evolutionary trends within the microbial community in the remote past," team leader Jure Piskur, a professor of molecular genetics at Lund University and the University of Nova Gorica, Slovenia, said in a news release.

"In addition, we can now use the knowledge we have obtained to develop new yeast strains, which could be beneficial for wine and beer fermentation and in biofuel production."